We have investigated the self-breaking mechanism of atomic scale Au nanocontacts at room temperature in air. In the conductance traces, we frequently observed traces showing both a 1G _0 (2e ~2/h) and 3G _0 plateaux, or only a 2G _0 plateau in the conductance regime below 3G _0. The statistical analysis showed a negative correlation between the appearance of 1G _0 and 2G _0 peaks, and a positive correlation between 1G _0 and 3G _0 peaks. This conductance behavior suggested that the symmetric triple atomic rows changed into a symmetric single row, while the asymmetric double rows broke without changing into a symmetric single row. The regular self-breaking process can be explained by the breaking of the thermodynamically stable Au nanocontacts which were formed during the self-breaking of the contacts.
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